1. Field of the Invention
The present invention relates to an electrochemical cell such as a non-aqueous electrolyte cell or an electric double-layer capacitor.
2. Description of the Related Art
An electrochemical cell has conventionally been used as, for example, a backup power supply for a clock function, a backup power supply for a memory of a semiconductor, a standby power supply for an electronic device such as a microcomputer or an IC memory, a cell for a solar watch or an electric power supply for driving a motor.
Although a button type electrochemical cell in disc form has been used in many occasions, when reflow soldering is performed on the electrochemical cell, it is necessary to previously weld a terminal or the like to a casing and, therefore, the number of parts is increased and production man-hour is also increased, to there by cause an increase of production cost. Further, it is necessary to provide a space for connecting the terminal on a substrate and, accordingly, there is a limitation on reduction of a size of the cell.
Still further, an improvement of thermal resistance is required in the electrochemical cell. This is because the electrochemical cell is mounted on the substrate by using reflow soldering. The term “reflow soldering” as used herein is intended to indicate a method of performing soldering by first applying in advance a solder cream or the like to a portion of a printed circuit board on which soldering is to be performed, next, placing a part on the portion, or, after the part is placed thereon, providing a small solder ball (solder bump) on the portion on which the soldering is to be performed and, then, passing the printed circuit board having the part thereon through a furnace which is set to have an atmosphere of high temperature inside such that the portion on which the soldering is to be performed is heated at a melting point or higher of solder, for example, a temperature in the range of from 200 to 260° C. allowing the solder to be melt.
In order to solve these problems, an electrochemical cell which uses a thermally resistant container as an outer sheath for containing an electrode and an electrolyte and is provided with a terminal has come to be studied (for example, refer to Patent Document 1).
Patent Document 1: JP-A No. 2001-216952 (Item Nos. 2 and 3; FIG. 1).
A problem to be solved by the present invention is that of dissolution of a positive electrode current collector.
A cross-sectional diagram of a conventional electrochemical cell is shown in FIG. 3.
In a case in which a material of a container 101 is prepared by using ceramics, the container 101 is made of ceramics such as alumina and is produced such that a green sheet is subjected to a printed-wiring treatment by using a metal having a high melting point such as tungsten, molybdenum, chromium, or alloys thereof and, then, fired.
On the side of a bottom face of the container 101, a positive electrode 106 is provided, and the positive electrode 106 is adhered to a positive electrode current collector 103 by using an electrically conductive adhesive 1111. The container 101 is sealed by a lid 102, and the container 101 and the lid 102 are joined to each other via a metallic ring 109. Further, a negative electrode 107 is adhered to the lid 102 by using an electrically conductive adhesive 1112. The positive electrode 106 and the negative electrode 107 are separated from each other by a separator 105. Still further, a connecting terminal A 1041 and a connecting terminal B 1042 are provided for connecting electrodes to an outside circuit.
However, when the conventional electrochemical cell is used at a relatively high voltage, for example, around 3 V, there is a problem in that the positive electrode current collector 103 which is in contact with the positive electrode is dissolved.
The reason is that, when the electrochemical cell is charged, a potential at the side of the positive electrode is elevated to a voltage of such an extent as dissolving the positive collector 103.
Under these circumstances, an object of the present invention is to provide an electrochemical cell which is easily produced, prevents dissolution of a positive electrode current collector and is capable of being used at a high voltage.